Liquid crystal display device

ABSTRACT

A liquid crystal display device includes first and second substrates, a liquid crystal layer, a plurality of video signal lines and scanning signal lines formed on the first delimiting pixel regions, a plurality of video signal line driving circuits, and a thin film transistor formed in the pixel regions, and driven by a scanning signal from a scanning signal line. A display area contains a plurality of the pixel regions and a first and second protection element lines are formed at a peripheral portion of the display area and connected to the video signal lines by first and second high-resistance elements. A first circuit board is electrically connected with a portion of the video signal line driving circuits and a second circuit board is electrically connected with another portion of the video signal line driving circuits.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/798,329,file Mar. 12, 2004, now U.S. Pat. No. 6,888,584, which is a continuationof application Ser. No. 09/973,775, filed Oct. 11, 2001, now U.S. Pat.No. 6,710,824, which is a continuation of application Ser. No.09/342,131 filed on Jun. 29, 1999, now U.S. Pat. No. 6,333,769, thecontents of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display device; and,more specifically, the invention relates to an in-plane field typeliquid crystal display device.

In general, an in-plane field type liquid crystal display device isprovided with a pixel electrode and a counter electrode spaced apartfrom the pixel electrode in each pixel area on a liquid-crystal-sidesurface of one of the transparent substrates which are opposed to eachother via a liquid crystal, and the optical transmittance of the liquidcrystal is controlled by means of an electric field which is selectivelygenerated between the pixel electrode and the counter electrode.

A liquid crystal display device of an active matrix type which adoptsthe in-plane field mode of operation includes, on a liquid-crystal-sidesurface of one of its transparent substrates, scanning signal linesextended in the x direction and juxtaposed in the y direction, countersignal lines extended in the x direction and juxtaposed in the ydirection, and video signal lines extended in the y direction andjuxtaposed in the x direction, and each area surrounded by adjacentscanning and counter signal lines and a pair of adjacent video signallines is formed as a pixel area. In each pixel area, there is athin-film transistor driven by the supply of a scanning signal from thescanning signal line and a pixel electrode to which a video signal issupplied from one of the video signal lines via the thin-filmtransistor. In this case, since a voltage corresponding to the videosignal relative to the counter electrodes is applied to the pixelelectrode, a reference voltage is applied to the counter electrode viathe counter signal line.

In such a liquid crystal display device, since its structure is suchthat the thin-film transistors are easily damaged by static electricity,it is indispensable to take measures against static electricity. As anattempt at taking measures against static electricity, there has been aproposal in which a protection element common line is formed to surrounda display area formed by an assembly of pixels, and scanning signallines and video signal lines are connected to the protection elementcommon line via non-linear elements at the intersections of the scanningand video signal lines and the protection element common line.

For example, a technique for taking measures against static electricityin a liquid crystal display device, which differs in structure from thein-plane field mode, is described in Japanese Patent Laid-Open No.9-90428. In accordance with this technique, as measures against staticelectricity, scanning signal lines and video signal lines are connectedto a common line via static protection elements. Although the staticprotection elements are formed of high-resistance elements so thatstatic electricity flows through the static protection elements, thescanning signal lines and the video signal lines are electricallyconnected via the static protection elements and the common line. Forthis reason, it has been found, when the liquid crystal display deviceis being driven by an external circuit, part of the video signals fromthe video signal lines flow into the static protection elements asleakage current and this leakage current flows into the counterelectrodes of the respective pixels via the common line, creatingproblems in that the image quality is degraded and the voltage at thevideo signal lines is lowered.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-describedproblems, and an object of the present invention is to provide atechnique which is capable of avoiding the occurrence of damage due tostatic electricity in a liquid crystal display device of the in-planefield type, which is provided with pixel electrodes and counterelectrodes on one substrate.

Another object of the present invention is to provide a liquid crystaldisplay device which is capable of avoiding the occurrence of leakagecurrent from scanning signal lines or video signal lines.

The above and other objects and novel features of the present inventionwill become apparent from the description given herein and theaccompanying drawings. A representative aspect of the inventiondisclosed in the present application will be summarized below.

In a liquid crystal display device, pixel areas which are surrounded byscanning signal lines, video signal lines and counter signal lines arearranged on a liquid-crystal-side surface of one of the transparentsubstrates opposed to each other across a liquid crystal, and therespective pixel areas include thin-film transistors driven by thesupply of scanning signals from the scanning signal lines, pixelelectrodes to which video signals from the video signal lines aresupplied via the respective thin-film transistors, and counterelectrodes spaced apart from the pixel electrodes and connected to thecounter signal lines. A common line is formed to surround a display areaformed by an assembly of the pixel areas, and the video signal lines andthe scanning signal lines are connected to the common line by non-linearelements at the intersections of the video and scanning signal lines andthe common line. The common line is connected to the counter signallines via high-resistance elements.

In the liquid crystal display device having the above-describedconstruction, even if leakage current due to scanning or video signalsflows via the non-linear elements, this leakage current can be preventedfrom flowing into the counter signal lines by the high-resistanceelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the essential construction of an embodimentof the liquid crystal display device according to the present invention;

FIG. 2 is a schematic diagram showing the embodiment of the liquidcrystal display device according to the present invention;

FIG. 3 is a plan view showing an example of the configuration of a pixelarea of the liquid crystal display device according to the presentinvention;

FIG. 4 is a schematic circuit diagram for use in describing problems;and

FIG. 5 is a graph showing the output voltage of an output circuit.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the liquid crystal display device according to thepresent invention will be described below with reference to theaccompanying drawings.

FIG. 2 is a schematic view showing the construction of the entire liquidcrystal display device according to the present invention. In thisembodiment, the present invention is applied to a liquid crystal displaydevice which adopts a so-called in-plane field mode of operation, whichis known to have a wide viewing angle.

A liquid crystal display panel 1 includes transparent substrates 1A and1B which are arranged opposite to each other across a liquid crystal andserve as a package. One of these transparent substrates (the lowersubstrate shown in FIG. 2, i.e. a transparent matrix substrate 1A) isformed to be slightly larger than the other transparent substrate (theupper substrate shown in FIG. 2, i.e. a transparent color filtersubstrate 1B), and both transparent substrates are arranged to be nearlyeven with each other at their lower and right-hand edges, as viewed inFIG. 2. Accordingly, the transparent substrate 1A is extended outward ofthe transparent substrate 1B at its left-hand and upper edges, as viewedin FIG. 2. As will be described later in detail, this outward extendedportion is an area in which gate driving circuits and drain drivingcircuits are mounted.

Pixels 2, which are arranged in a matrix array, are formed in an area inwhich the transparent substrates 1A and 1B are superimposed on eachother. The pixels 2 are formed in areas, each of which is surrounded byadjacent ones of scanning signal lines 3, which are extended in the xdirection and juxtaposed in the y direction, as viewed in FIG. 2, andadjacent ones of video signal lines 4, which are extended in the ydirection and juxtaposed in the x direction. Each of the pixels 2 isprovided with at least a switching element TFT, which is driven by thesupply of a scanning signal from one of the adjacent scanning lines 3,and a pixel electrode to which a video signal supplied from one of theadjacent video signal lines 4 is applied via this switching element TFT.

As described above, each of the pixels 2 adopts the so-called horizontalelectric field system, and, as will be described later in detail, isprovided with a reference electrode and an additional capacitive elementin addition to the above-mentioned switching element TFT and pixelelectrode. Each of the scanning signal lines 3 is extended outward ofthe transparent substrate 1B at its one end (the left-hand end as viewedin FIG. 2) and is connected to the output terminal of a correspondinggate driving circuit (IC) 5 mounted on the transparent substrate 1A. Inthis construction, a plurality of gate driving circuits are disposedalong one edge of the substrate 1A, and the scanning signal lines 3 aregrouped into pairs of adjacent lines and each of the grouped pairs isconnected to a proximate one of the gate driving circuits 5.

Similarly, each of the video signal lines 4 is extended outward of thetransparent substrate 1B at its one end (the upper end as viewed in FIG.2) and is connected to the output terminal of a corresponding draindriving circuit (IC) 6 mounted on the transparent substrate 1A. In thisconstruction, a plurality of drain driving circuits 6 are disposed alongone edge of the substrate 1A, and the video signal lines 4 are groupedinto pairs of adjacent lines and each of the grouped pairs is connectedto a proximate one of the drain driving circuits 6.

A printed circuit board (control circuit board) 10 is arranged on theside of the liquid crystal display panel 1 on which the gate drivingcircuits 5 and the drain driving circuits 6 are mounted in theabove-described manner, and a control circuit 12 for supplying inputsignals to the gate driving circuits 5 and the drain driving circuits 6is mounted on the printed circuit board 10 in addition to a power supplycircuit 11 and other circuits. Signals from the control circuit 12 aresupplied to the gate driving circuits 5 and the drain driving circuits 6via flexible printed wiring boards (a gate circuit board 15, a draincircuit board 16A and a drain circuit board 16B).

Specifically, a flexible printed wiring board (the gate circuit board15) which is provided with terminals opposed and connected to the inputterminals of the respective gate driving circuits 5 is arranged on theside of the gate driving circuits 5. A portion of the gate circuit board15 is formed to extend toward the printed circuit board 10, and theextended portion is connected to the printed circuit board 10 via aconnecting part 18. The output signals from the control circuit 12mounted on the printed circuit board 10 are inputted to the respectivegate driving circuits 5 via a wiring layer on the printed circuit board10, the connecting part 18 and a wiring layer on the gate circuit board15.

The drain circuit boards 16A and 16B, each of which is provided withterminals opposed and connected to the input terminals of the respectivedrain driving circuits 6, are arranged on the side of the drain drivingcircuits 6. Portions of the drain circuit boards 16A and 16B are formedto extend toward the printed circuit board 10, and the extended portionsare connected to the printed circuit board 10 via connecting parts 19Aand 19B, respectively. The output signals from the control circuit 12mounted on the printed circuit board 10 are inputted to the draincircuit boards 16A and 16B via the wiring layer on the printed circuitboard 10, the respective connecting parts 19A and 19B, and wiring layerson the respective drain circuit boards 16A and 16B.

The drain circuit boards 16A and 16B for the drain driving circuits 6are provided as two separate circuit boards, as shown in FIG. 2. This isintended to prevent, for example, harmful effects caused by thermalexpansion due to an increase in length in the x direction of FIG. 2 ofeither of the drain circuit boards 16A or 16B which accompanies anincrease in the size of the liquid crystal display panel 1. The outputsignals from the control circuit 12 mounted on the printed circuit board10 are inputted to the corresponding drain driving circuits 6 via theconnecting part 19A of the drain circuit board 16A and the connectingpart 19B of the drain circuit board 16B. In addition, a video signal issupplied from a video signal source 22 to the printed circuit board 10,through a cable 23 via an interface circuit board 24, and is inputted tothe control circuit 12 mounted on the printed circuit board 10.

In FIG. 2, the liquid crystal display panel 1, the gate circuit board15, the drain circuit boards 16A and 16B and the printed circuit board10 are shown to be positioned in approximately the same plane. Actually,the printed circuit board 10 is bent at a portion where the gate circuitboard 15 and the drain circuit boards 16A and 16B are mounted, and ispositioned at approximately right angles to the liquid crystal displaypanel 1. This construction is intended to reduce the area of theso-called frame, which is the area between the outline of the outer edgeof the liquid crystal display device and the outline of its displayportion, and by reducing this frame area, it is possible to obtain theeffect of increasing the area of the display portion with respect to theouter frame.

FIG. 3 is a plan view showing in detail the construction of a pixelarea. Referring to FIG. 3, the scanning signal line 3 and a countersignal line 50, which are extended in the x direction, are formed on aprincipal surface of the transparent substrate 1A. The area surroundedby each of these signal lines 3 and 50 and adjacent video signal lines 4(to be described later), which are extended in the y direction, forms apixel area. In other words, in this embodiment, the counter signal line50 is formed to run between the scanning signal lines 3 in parallel withthe same, and pixel areas are respectively formed to extend in the ±ydirections from each counter signal line 50.

With this construction, it is possible to reduce the number of thecounter signal lines 50 juxtaposed in the y direction to approximatelyhalf of the conventionally required number, whereby it is possible toassign the areas occupied by the counter signal lines 50 to the pixelareas and increase the total area of the pixel areas. In each of thepixel areas, for example, three counter electrodes 50A, which extend inthe y direction, are formed at equal intervals integrally with a countersignal line 50. These counter electrodes 50A are not connected to, butextend to positions close to, the scanning signal line 3, and theoutside two counter electrodes 50A are arranged adjacent to therespective video signal lines 4, and the remaining one counter electrode50A is positioned in the center therebetween.

Furthermore, an insulation film made of, for example, silicon nitride isformed to cover the scanning signal lines 3, the counter signal lines 50and the counter electrodes 50A, over the principal surface of thetransparent substrate 1A on which the scanning signal lines 3 and othersare formed in the above-described manner. This insulation film functionsas an interlayer insulation film for insulating the video signal lines 4from the scanning signal lines 3 and the counter signal line 50, andalso functions as a gate insulation film for the thin-film transistorTFT and as a dielectric film for a storage capacitor Cstg.

On the surface of the insulation film, a semiconductor layer 51 isformed in an area in which the thin-film transistor TFT is formed. Thissemiconductor layer 51 is made of, for example, amorphous Si, and isformed to be superimposed on the scanning signal line 3 in a portionclose to one of the video signal lines 4 which will be described later.Thus, part of the scanning signal line 3 serves as the gate electrode ofthe thin-film transistor TFT. The video signal lines 4, which areextended in the y direction and juxtaposed in the x direction, areformed on the surface of the insulation film. Each of the video signallines 4 is integrally provided with a drain electrode 4A which is formedto extend into a portion of the surface of the semiconductor layer 51which constitutes the thin-film transistor TFT.

Furthermore, a pixel electrode 53, which is connected to a sourceelectrode 53A of the thin-film transistor TFT, is formed on the surfaceof the insulation film in the pixel area. This pixel electrode 53 isformed to have respective portions which extend in the y direction inthe center between respective pairs of the counter electrodes 50A.Specifically, one end of the pixel electrode 53 also serves as thesource electrode 53A of the thin-film transistor TFT, and the pixelelectrode 53 has a first portion which extends in the y direction towardthe counter signal line 50, a second portion which extends in the xdirection along the counter signal line 50, and a third portion whichextends in the y direction, thereby forming a U-shape. The portion ofthe pixel electrode 53 which is superimposed on the counter signal line50 constitutes a part of the storage capacitor Cstg, which uses theabove-described insulation film as the dielectric film, in the regionbetween the portion and the counter signal line 50. The storagecapacitor Cstg serves to store video information in the pixel electrode53 for a long time, for example, when the thin-film transistor TFT isoff.

The surface of the semiconductor layer 51 which corresponds to theinterface between the drain electrode 4A and the source electrode 53A ofthe thin-film transistor TFT is doped with phosphorus (P) to form ahigh-concentration layer, thereby providing ohmic contact at each of thedrain electrode 4A and the source electrode 53A. The high-concentrationlayer is formed over the entire surface of the semiconductor layer 51,and after the drain electrodes 4A and the source electrodes 53A havebeen formed, these electrodes 4A and 53A are used as a mask to etch theportion of the high-concentration layer other than the area in which theelectrodes 4A and 53A are formed, thereby forming the above-describedconstruction.

Then, a protective film made of, for example, silicon nitride is formedover the insulation film on which the thin-film transistors TFT, thevideo signal lines 4, the pixel electrodes 53 and the storage capacitorsCstg are formed in the above-described manner, and an alignment film isformed over the protective film, to constitute the so called lowersubstrate of the liquid crystal display panel 1.

Although not shown, a black matrix (denoted by reference numeral 54 inFIG. 3), which has apertures in portions corresponding to the respectivepixel areas, is formed in a liquid-crystal-side portion of thetransparent substrate (color filter substrate) 1B which constitutes theso-called upper substrate. Furthermore, color filters are formed tocover the apertures formed in the portions of the black matrix 54 whichcorrespond to the respective pixel areas. These color filters havecolors which differ between adjacent pixel areas in the x direction, andthe respective color filters have boundaries on the black matrix 54. Aflat film made of resin or the like is formed over the surface on whichthe black matrix 54 and the color filters are formed in this manner, andan alignment film is formed over the surface of the flat film.

FIG. 1 is a diagram showing one embodiment of a static protectioncircuit formed on the transparent substrate 1A. The static protectioncircuit shown in FIG. 1 is formed on the transparent substrate 1A in thearea between a display area (denoted by symbol AR in FIG. 1) made up ofan assembly of pixel areas and a shielding material (denoted by symbolSD in FIG. 1) for sealing a liquid crystal in the space between thematrix substrate 1A and the color filter substrate 1B.

Protection element common lines 71A and 71B are formed to intersect thevideo signal lines 4 above and below the display area, respectively.These protection element common lines 71A and 71B are formed of the samematerial as and by the same process as, for example, the scanning signallines 3 and the counter signal lines 50. Accordingly, the protectionelement common lines 71A and 71B are formed to intersect the videosignal lines 4 via the insulation film. Non-linear elements NL forproviding connection between each of the protection element common lines71A and 71B and the video signal lines 4 are formed at the intersectionsthereof as protection elements for preventing static damage. Forexample, the non-linear elements NL above the display area are arrangedon odd-numbered video signal lines from the left as viewed in FIG. 1,while the non-linear elements NL below the display area are arranged oneven-numbered video signal lines from the left. The reason why thearrangements of the non-linear elements NL differ between adjacent onesof the video signal lines 4 is that the video signal lines 4 and thescanning signal lines 3 can be smoothly inspected for disconnections orthe like in the manufacturing process of the liquid crystal displaydevice.

Each of the non-linear elements NL is made of, for example, two diodes,and one of the diodes is connected to the signal supply side of thevideo signal line 4 as an anode and to the protection element commonline 71A (or 71B) as a cathode, while the other diode is connected tothe protection element common line 71A (or 71B) as an anode and to thedisplay area side of the video signal line 4 as a cathode. Each of thediodes is formed in parallel with the thin-film transistor TFT in eachof the pixel areas, and has approximately the same construction as thethin-film transistor TFT except that the gate electrode and the sourceelectrode are connected to each other.

Instead of the diodes, high-resistance elements which allow staticelectricity to flow therethrough may be used as the protection elements.Such high-resistance elements may be of the type in whichinterconnection lines are locally narrow in line width orinterconnection lines are prolonged by being bent, or intrinsicsemiconductors may also be used.

A protection element common line 71C is formed to intersect the scanningsignal lines 3 on the left-hand side of the display area as viewed inFIG. 1 (on the signal supply side of the scanning signal lines 3). Theprotection element common line 71C is formed of the same material as andby the same process as, for example, the video signal lines 4.Accordingly, the protection element common line 71C is formed tointersect the scanning signal lines 3 via the insulation film.Non-linear elements NL are formed at the intersections of the protectionelement common line 71C and the scanning signal lines 3 as protectionelements for providing connection between the protection element commonline 71C and the scanning signal lines 3.

Each of the non-linear elements NL is made of, for example, two diodes,and one of the diodes is connected to the signal supply side of thescanning signal line 3 as an anode and to the protection element commonline 71C as a cathode, while the other diode is connected to theprotection element common line 71C as an anode and to the display areaside of the scanning signal line 3 as a cathode. Each of the diodes isformed in parallel with the thin-film transistor TFT in each of thepixel areas, and has approximately the same construction as thethin-film transistor TFT except that the gate electrode and the sourceelectrode are connected to each other.

Each of the counter signal lines 50, which are extended in the xdirection and juxtaposed in the y direction in the display area, areconnected to counter signal common lines 50B and 50C at its oppositeends. The counter signal common lines 50B and 50C are formed of the samematerial as and by the same process as the counter signal lines 50. Thecounter signal common lines 50B and 50C are respectively provided withsignal supply terminals, and counter voltages are respectively appliedfrom the signal supply terminals to the counter electrodes 50A in thepixel areas via the counter signal common lines 50B and 50C and thecounter signal lines 50. In this manner, by supplying the countervoltages from the opposite sides of the counter signal lines 50, it ispossible to supply signals to the counter electrodes 50A disposed in therespective pixel areas, without causing waveform distortions of thesignals of the counter voltages. In this case, in applications of thepresent invention, it goes without saying that the counter voltage neednot necessarily be supplied from the opposite sides of the countersignal lines 50, but may be supplied from either side of the countersignal lines 50.

A problem encountered when a counter signal is supplied to protectionelement common lines will be described below with reference to FIG. 4.FIG. 4 diagrammatically represents the relationship between protectionelement common line, video signal line, scanning signal line andprotection element. In FIG. 4, for the sake of explanation of theproblem, a protection element common line 71A′ and a protection elementcommon line 71C′ are connected to each other via no high-resistanceelement. A voltage V2 of a counter signal is supplied from a terminalVCOM.

Non-linear elements NL1 and NL2 are disposed as protection elementsbetween the protection element common line 71A′ and the video signalline 4. An output circuit AMP1, which is a driving circuit, is connectedto the video signal line 4 and, for example, a voltage VOUT1 is suppliedto the video signal line 4 as a video signal. In addition, non-linearelements NL3 and NL4 are disposed as protection elements between theprotection element common line 71C′ and the scanning signal line 3. Adriving circuit AMP2 is connected to the scanning signal line 3, and,for example, a voltage VOUT3 is supplied to the scanning signal line 3as a scanning signal. Each of the non-linear elements NL1, NL2, NL3 andNL4 is formed by a diode in which the gate electrode and the sourceelectrode of a thin-film transistor is connected to each other, and itsON resistance is approximately 10 MΩ.

In general, the output circuit AMP1 is a buffer amplifier (voltagefollower) which outputs a voltage equal to an input voltage VIN as anoutput voltage VOUT, but as shown in FIG. 5, the voltage VOUT changes tothe input voltage VIN in a predetermined time owing to the capacitanceof the video signal line 4 or the like. At this time, the outputresistance value of the output circuit AMP1 changes from approximately 1kΩ to approximately several MΩ. If the output resistance value of theoutput circuit AMP1 is approximately 1 kΩ, it can be neglected becauseit is significantly smaller than the ON resistance of any of thenon-linear elements NL1, NL2, NL3 and NL4. However, if the outputresistance value of the output circuit AMP1 changes to several MΩ, theratio of the output resistance value to the ON resistance of any of thenon-linear elements NL1, NL2, NL3 and NL4 becomes approximately 1:10which causes a problem. For example, in FIG. 4, if the ON resistance ofthe non-linear element NL1 is 10 MΩ and the output resistance value ofthe output circuit AMP1 is 10 MΩ, a voltage VOUT′, which is equivalentto a potential difference (VIN−VCOM)×( 9/10) between a voltage V2supplied from the terminal VCOM to the protection element common line71A′ and the input voltage VIN of the output circuit AMP1, is outputtedto the video signal line 4.

To solve the above-described problem, the protection element common line71A which is formed to intersect the video signal lines 4 is connectedat its one end to the counter signal common line 50B via ahigh-resistance element 80, and at the other end to the counter signalcommon line 50C via a high-resistance element 81. The protection elementcommon line 71B which is formed to intersect the video signal lines 4 isconnected at its one end to the counter signal common line 50B via ahigh-resistance element 82, and at the other end to the counter signalcommon line 50C via a high-resistance element 83. Similarly, theprotection element common line 71C which is formed to intersect thescanning signal lines 3 is connected at its one end to the countersignal common line 50B via a high-resistance element 84, and at theother end to the counter signal common line 50B via a high-resistanceelement 85.

In the static protection circuit which is constructed in theabove-described manner, even if static electricity penetrates from thesignal supply sides of the scanning signal lines 3, the video signallines 4, and the counter signal common lines 50B and 50C, the staticelectricity is diffused into the protection element common lines 71A,71B, 71C and the like via the non-linear elements NL, whereby the staticelectricity can be kept from penetrating the thin-film transistors TFTin the respective pixel areas. In addition, during the addressing of theliquid crystal display device, even if leakage current due to a videosignal flows through any of the non-linear elements NL, this leakagecurrent can be restrained from flowing through the counter signal commonlines 50B and 50C by the high-resistance elements 80, 81, 82 and 83, sothat it is possible to ameliorate the problem that the output voltagesfrom the driving circuits are lowered. Similarly, even if leakagecurrent due to a scanning signal flows through any of the non-linearelements NL, this leakage current can be prevented from flowing throughthe counter signal common line 50B by the high-resistance elements 84and 85.

Each of the high-resistance elements 80, 81, 82, 83, 84 and 85 is madeof, for example, two diodes which are connected in parallel and areopposed to each other in polarity, as shown in FIG. 1. In this case,each of the diodes is formed in parallel with the thin-film transistorTFT in each of the pixel areas, and has approximately the sameconstruction as the thin-film transistor TFT except that the gateelectrode and the source electrode are connected to each other. Thehigh-resistance elements 80, 81, 82, 83, 84 and 85 may be of the type inwhich interconnection lines are locally narrow in line width or in whichinterconnection lines are extended in length by being bent, or intrinsicsemiconductors may also be used.

As is apparent from the foregoing description, in accordance with theliquid crystal display device according to the present invention, it ispossible to prevent static damage and it is also possible to avoid theoccurrence of leakage current due to signals flowing from scanningsignal lines or video signal lines to counter signal lines.

1. A liquid crystal display device comprising: a first substrate; asecond substrate; a liquid crystal layer interposed between said firstsubstrate and said second substrate; a plurality of video signal linesand scanning signal lines formed on said first substrate, and delimitingpixel regions; plural video signal line driving circuits electricallyconnected with said video signal lines; a thin film transistor formedabove each of said pixel regions, and driven by a scanning signal fromscanning signal line for supplying a video signal from one of the videosignal lines to a pixel electrode; a display area containing a pluralityof said pixel regions; a protection element line formed above aperipheral portion of said display area, and being connected to at leastone of said video signal lines by at least one protection element; aplurality of counter signal lines formed above said display area andconnected to a storage capacitor; at least one common line formed abovea peripheral portion of said display area and electrically connectedwith at least one of said counter signal lines; a first circuit boardelectrically connected with a plurality of said plural video signal linedriving circuits for supplying a video signal to a left side of saiddisplay area; and a second circuit board electrically connected withanother plurality of said plural video signal line driving circuits forsupplying a video signal to a right side of said display area; whereinsaid at least one common line is electrically connected with saidprotection element line by at least one high-resistance element.
 2. Aliquid crystal display device according to claim 1, wherein said atleast one protection element has a gate electrode connected to a sourceelectrode.
 3. A liquid crystal display device according to claim 1,wherein said at least one protection element is formed by at least onediode in which a gate electrode and a source electrode of a thin-filmtransistor is connected to each other.
 4. A liquid crystal displaydevice comprising: a first substrate; a second substrate; a liquidcrystal layer interposed between said first substrate and said secondsubstrate; a plurality of video signal lines and scanning signal linesformed on said first substrate, and delimiting pixel regions; pluralvideo signal line driving circuits electrically connected with saidvideo signal lines; a thin film transistor formed in each of said pixelregions, and driven by a scanning signal from a scanning signal line forsupplying a video signal from one of the video signal lines to a pixelelectrode; a display area containing a plurality of said pixel regions;a protection element line formed at a peripheral portion of said displayarea, and being connected to at least one of said video signal lines byat least one first high-resistance element; a plurality of countervoltage lines formed above said display area and connecting a commonline at a left side and a right side of said display area and a storagecapacitor at said pixel regions; a common line electrically connected tosaid protection element line by at least one second high-resistanceelement; a first circuit board electrically connected with a pluralityof said plural video signal line driving circuits; and a second circuitboard electrically connected with another plurality of said plural videosignal line driving circuits.
 5. A liquid crystal display deviceaccording to claim 4, wherein at least one of said first and secondhigh-resistance elements has a gate electrode connected to a sourceelectrode.
 6. A liquid crystal display device according to claim 4,wherein at least one of said first and second high-resistance elementsis formed by at least one diode in which a gate electrode and a sourceelectrode of a thin-film transistor is connected to each other.
 7. Aliquid crystal display device according to claim 4, wherein said firstand second high-resistance elements have a same configuration.